Gurbatov S.N., Mainardi F., Moshkov A.Yu., Tampieri F. «Density distribution in a turbulent flow with strong friction» Труды (пятой) научной конференции по радиофизике, посвященной 100-летию со дня рождения А.А. Андронова. 7 мая 2001 г., с. 230-231 (2001)

Tanter Mickael, Fink Mathias «Time reversal of acoustic waves in the nonlinear regime: application to harmonic imaging in medical ultrasound» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 5-11 (2005)

Harmonic imaging coupled to the use of contrast agents is a topic of wide interest in ultrasonic medical imaging. Images are built at twice the excitation frequency that corresponds to the resonance frequency of the bubbles embedded in the medium. Consequently, the contrast becomes important between areas of low and high concentration of bubbles. However, at a high mechanical index, the harmonic components of backscattered echoes depends on the intrinsic nonlinear properties of tissues as well as the bubble's resonance. The focused beam is generating harmonics during its nonlinear propagation. It results in a degradation of the harmonic image contrast. Time reversal is an elegant way to find the emission codes allowing us to cancel the harmonic components due to nonlinear propagation of the ultrasonic beam and so to recover an optimal image contrast. Indeed, the wave equation in a nonlinear regime remains time reversal invariant: in the absence of bubbles, if the backscattered echoes are time-reversed and reemitted by the array, the harmonic components of the resulting wavefront are transferred back to the fundamental frequency during propagation. Another way to calculate the optimal waveforms to be emitted for harmonics cancellation consists to achieve the first step of the time reversal experiment using simulations of the nonlinear wave propagation. The waveforms deduced from a KZK or finite differences code can be used as calibrated signals for the in vivo experiments. Experiments conducted with 1D-linear arrays illustrate these cancellation techniques. The contrast enhancement obtained emphasizes the great potential of fully programmable emission boards in multi-channels systems.

Catheline Stefan, Tanter Mickael, Gennisson Jean-Luc, Fink Mathias «Nonlinear propagation of shear waves in soft solids» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 81-85 (2005)

Transient elastography has shown its efficiency to map the elastic properties of soft tissues. Now like other elastic imaging techniques (sonoelastography or magnetic resonance elastography) transient elastography is faced to the following problem: in order to properly discriminate tumors, additional information such as viscosity, anisotropy or nonlinearity is needed. If nonlinearity has long been studied in metals, crystals or rocks, only a few experimental works are found in the literature concerning soft tissues and none on shear waves. Thanks to the ultrafast scanner that can map the displacement field of shear waves, we present in this paper an overview of three experiments that allow to illustrate and quantify the nonlinear behavior of soft tissue phantoms. In the first one, a static stress is applied on an Agar-gelatin based sample. The change on the shear wave speed characterizes the nonlinear elastic Landau moduli (A = 50 kPa, B = 7 GPa, C = 11 GPa). The surprising difference found between these constants are thought to be closely related to the huge difference between the linear Lame coefficients (λ>>μ). It is the acoustoelasticity experiment. In the second one, we present an experimental observation of a shock shear wave. The very weak Young’s modulus of the tissue phantom allows one to generate plane shear wave with a Mach number as high as unity. In this extreme configuration, the agreement with the numerical simulation of the modified Burgers equation is remarkable. It is the finite-amplitude shear wave experiment. At last, the interaction between two plane transverse waves with frequencies ω1 and ω2 is carefully studied. Harmonics and secondary waves are created during the propagation at the frequencies (3ω1, 3ω2, ω1+2ω2, ω1–2ω2, ω2+2ω1, ω 2–2ω1). It is the nonlinear interaction experiment. The nonlinear coefficients deduced from the two latter experiments are comparable to the order of magnitude of the Landau coefficients found from the first experiment.

Tournat V., Gusev V.E., Zaitsev V.Yu., Nazarov V.E., Castagnede B., Bequin Ph., Inserra C. «Nonlinear acoustic effects in unconsolidated granular media» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 86-92 (2005)

This paper deals with various manifestations of classical and non classical nonlinear acoustic effects that have been observed recently in unconsolidated assemblages of glass beads: operation of the parametric antenna with shear pump waves, non monotonous amplitude dynamics of the longitudinal second harmonic generated from a shear fundamental wave, cross-modulation of propagating waves. Theoretical interpretations of each of these non linear effects demonstrate the important role of the so-called weak contacts, i.e. contacts that support weaker static loads than the average one in the medium. In contrast, the linear wave propagation is mainly affected by the average and strong contacts. As a consequence, nonlinear acoustic methods are found to be much more sensitive than the linear methods for the evaluation of the granular materials in general, and may contribute to a better understanding of their peculiar properties.

Зайцев В., Назаров В., Tournat V., Gusev V., Castagnede B. «Люксембург-горьковский эффект в гранулированной среде» Труды (восьмой) научной конференции по радиофизике, посвященной 80–летию со дня рождения Б.Н.Гершмана. 7 мая 2004 г., с. 209-211 (2004)